Diesel Turbine SCR Catalyst

ABSTRACT

A system for treating exhaust gases from an engine is described. The system includes, the exhaust gases routed from the engine to atmosphere through an exhaust passage, the system comprising: an injector directing a spray of reductant into the exhaust gases routed from the engine to atmosphere; an exhaust separation passage that separates an exhaust gas flow received from the engine into a plurality of separate exhaust gas flows; a plurality of oxidation catalysts, each of which receives one of the plurality of separate exhaust gas flows; a flow combining passage that receives the plurality of separate exhaust gas flows and combines them into a re-combined exhaust gas flow; a turbocharger that receives the re-combined exhaust gas flow from the flow combining passage; and a selective catalytic reduction catalyst positioned downstream of the turbocharger.

BACKGROUND AND SUMMARY

An engine exhaust system may include various components to enhanceengine operation and reduce emissions. These may include selectivecatalytic reduction (SCR) catalysts, oxidation catalysts, NOx traps,turbochargers, exhaust gas recirculation, etc.

One example of such an engine exhaust system is described in U.S.2006/0080953. In the exhaust system described in U.S. 2006/0080953, areducing agent is supplied to an exhaust gas stream upstream of aturbocharger that aids in the breakdown and distribution of the reducingagent (suspended within the exhaust gas stream) prior to the exhaust gasstream reaching a downstream oxidation and SCR catalyst. Furthermore, inthis example, multiple separate exhaust gas flows from multiplecylinders are funneled through individual oxidation catalysts, each ofthe individual oxidation catalysts arranged in an individual tube of anexhaust manifold. Thus, as described in U.S. 2006/0080953, separateexhaust flows are ejected by an engine and immediately passed throughseparate oxidation catalysts. The separate exhaust flows are thencombined into a single exhaust gas flow and injected with a liquidreductant prior to reaching a downstream mixer.

The inventors herein have recognized numerous issues with the aboveapproach. In particular, because the exhaust gases are deliveredseparately from the cylinders to the upstream catalyst 5, the packagingof multiple oxidation catalysts within individual exhaust manifold tubesmay increase packaging constraints on other vital engine components.Correspondingly, the ease of manufacture of such an exhaust system maybe reduced and the related manufacturing costs may be increased.

In one approach, a system for treating exhaust gases from an engine, theexhaust gases routed from the engine to atmosphere through an exhaustpassage, is provided. The system comprises an injector directing a sprayof reductant into the exhaust gases; a first flow combining passage thatcombines exhaust gas from a plurality of cylinders; an exhaustseparation passage, downstream of the first combining passage, thatseparates an exhaust gas flow into a plurality of separate exhaust gasflows; a plurality of oxidation catalysts, each of which receives one ofthe plurality of separate exhaust gas flows; a second downstream flowcombining passage that receives the plurality of separate exhaust gasflows and combines them into a re-combined exhaust gas flow; aturbocharger that receives the re-combined exhaust gas flow; and aselective catalytic reduction catalyst positioned downstream of theturbocharger.

In this way, by first combining and then separating the exhaust gasesejected by the engine prior to injecting a liquid reductant and passingthe re-combined exhaust gas flow through the turbocharger, the exhausttreatment system may be more compactly and flexibly packaged and maythus allow for more flexibility in the arrangement and packaging ofother vital vehicle components. Correspondingly, the ease and cost ofmanufacturing such an exhaust treatment system may be reduced.Furthermore, by first combining the exhaust gases ejected by individualcylinders, separating the resulting single exhaust gas flow and thenre-combining the exhaust gas flow into a re-combined exhaust gas flow,the geometrical relationship between the plurality of separated exhaustgas flows upon being re-combined by the second downstream flow combiningpassage may be configured such that a more turbulent re-combined flowmay be realized. This increased turbulence within the re-combined flowmay increase the breakdown (into ammonia) and distribution of a liquidreductant (within the re-combined exhaust gas flow) injected therein.

By arranging oxidation catalysts upstream of a turbocharger, theoxidation catalysts and SCR catalyst can be located in warmer locations(i.e., closer to the engine) and may thus allow for both the oxidationcatalysts and the SCR catalyst to reach light-off temperature morequickly. As such, fewer emissions may be released to atmosphere duringthe initial “warm-up” phase of the engine. Additionally, this increasedthermal efficiency may reduce the need for parasitic rapid warmingconventions (that reduce overall fuel economy) that may use fuel forheating purposes.

Another potential advantage of the present disclosure is that, in someembodiments, the impingement of the exhaust gases upon the rotatingblades integral and internal to the turbocharger may aid in thebreakdown of the injected urea (suspended within the exhaust gases) intoammonia and in the uniformity of distribution of the ammonia dropletssuspended within the exhaust gases. Likewise, the SCR washcoat coatingthe blades of the turbocharger may further enhance the breakdown of ureainto ammonia. Thus, the overall efficiency of NOx removal by the SCRcatalyst arranged downstream of the turbocharger may be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exhaust system for transporting and treatingexhaust gases produced by an internal combustion engine according to anembodiment of the present disclosure.

FIG. 2 illustrates a side view of the exhaust system of FIG. 1 ingreater detail as a longitudinal cross-section according to anembodiment of the present disclosure.

FIG. 3 illustrates a process flow for transporting and treating exhaustgases via the exhaust system of FIG. 1 according to an embodiment of thepresent disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates an exhaust system 100 for transporting and treatingexhaust gases produced by internal combustion engine 110. As onenon-limiting example, engine 110 includes a diesel engine that producesa mechanical output by combusting a mixture of air and diesel fuel.Alternatively, engine 110 may include other types of engines such asgasoline burning engines, among others. Further, engine 110 may beconfigured in a propulsion system for a vehicle. Alternatively, engine110 may be operated in a stationary application, for example, as anelectric generator. While exhaust system 100 may be applicable tostationary applications, it should be appreciated that exhaust system100 as described herein, is particularly adapted for vehicleapplications.

Exhaust system 100 may include one or more of the following: an exhaustmanifold 120 for receiving exhaust gases produced by one or morecylinders of engine 110, oxidation catalysts 134 and 136 arrangeddownstream of exhaust manifold 120 for reducing unburned hydrocarbonsand carbon monoxide in the exhaust gas flow stream, a turbocharger 166that may receive exhaust gas flow streams from oxidation catalysts 134and 136, an injector 132 that may inject a liquid reductant into theexhaust gases upstream of turbocharger 166, a selective catalyticreduction (SCR) catalyst 140 located downstream of turbo 166, and anoise suppression device 150 arranged downstream of SCR catalyst 140.

As illustrated in FIG. 1, a diesel particulate filter (DPF) 142 may belocated downstream of SCR catalyst 140. In other embodiments, DPF 142may be located upstream of SCR catalyst 140 or arranged downstream ofturbocharger 166 and upstream of an additional diesel particulatefilter. In yet other embodiments, a diesel particulate filter may beintegral to SCR catalyst 140. Additionally, exhaust system 110 mayinclude a plurality of exhaust pipes or passages for fluidicallycoupling the various exhaust system components. For example, asillustrated by FIG. 1, exhaust manifold 120 may be fluidically coupledto oxidation catalysts 134 and 136 by one or more of exhaust passages162, 164, and 165. Similarly, SCR catalyst 140 may be fluidicallycoupled to noise suppression device 150 by exhaust passages 168 and 169(via DPF 142). Finally, exhaust gases may be permitted to flow fromnoise suppression device 150 to the surrounding ambient environment viaexhaust passage 170. Note that while not illustrated by FIG. 1, exhaustsystem 100 may include a particulate filter arranged upstream of SCRcatalyst 140. Furthermore, it should be appreciated that exhaust system100 may include two or more catalysts.

SCR catalyst 140 may reduce the amount of NOx that is ultimatelydischarged to the surrounding environment during operation of theengine. The SCR catalyst may utilize a liquid reductant such as anaqueous urea solution that is injected into the exhaust gases upstreamof the SCR catalyst. Prior to reaching the SCR catalyst, the waterdroplets within the injected solution may evaporate. The remaining ureacomponent then hydrolyzes and decomposes into ammonia which then entersthe SCR catalyst via the exhaust gas flow stream. A catalytic coatingwithin the SCR catalyst facilitates a reaction between the NOx componentof the exhaust gas flow stream and the ammonia to break down the NOxinto water vapor and nitrogen gas. The efficiency of this NOx reductionmay be directly proportional to the degree of vaporization of theaqueous urea solution and uniformity of the distribution of theresulting ammonia within the engine exhaust gases upstream of the SCRcatalyst.

As illustrated in FIG. 1, exhaust gases ejected by engine 110 (viamanifold 120) may enter an exhaust treatment region 135 where theexhaust gases may first be combined by first flow combining passage 164.The exhaust gas flow may then be separated into two or more separatedexhaust gas flows via exhaust separation passage 165. In otherembodiments, the exhaust gas flow may be separated into three or fourseparate exhaust gas flows by exhaust separation passage 165, forexample. Although illustrated as including two branches that have twopassages that are substantially perpendicular to each otherrespectively, other embodiments may include an exhaust separationpassage that has multiple branches that each consist of one passage (ormultiple passages) that has multiple curves and/or bends and/or isvariable in its cross-sectional area/shape.

The separated exhaust gas flows may then be received by oxidationcatalysts 134 and 136. In other embodiments, the separated exhaust gasflows may be received by three or four oxidation catalysts, for example.By utilizing multiple oxidation catalysts and locating them upstream ofturbocharger 166, oxidation catalysts 134 and 136 and SCR catalyst 140may be arranged in closer proximity to engine 110. Thus, both theoxidation catalysts and the SCR catalyst, by virtue of being in closerproximity to engine 110, may be effectively located in warmer locations.Additionally, by first combining the exhaust gases ejected by individualcylinders, separating the resulting single exhaust gas flow and thenre-combining the exhaust gas flow into a re-combined exhaust gas flow,the geometrical relationship between the plurality of separated exhaustgas flows upon being re-combined by the second downstream flow combiningpassage may be configured such that a more turbulent re-combined flowmay be realized. This increased turbulence within the re-combined flowmay increase the breakdown (into ammonia) and distribution of a liquidreductant (within the re-combined exhaust gas flow) injected therein.

During the period of time between initial start-up of a vehicle and thetime at which an exhaust treatment system that includes an oxidationcatalyst and an SCR catalyst reaches operating temperature (i.e.,light-off temperature), emissions containing higher levels of NOx andcarbon oxides may be passed to atmosphere. Therefore, by dividing theoxidation catalyst function among more than one oxidation catalyst andlocating the multiple oxidation catalysts upstream of the turbocharger,the oxidation catalysts and SCR catalyst may be arranged in closerproximity to the engine (i.e., as opposed to a linear arrangement with asingle oxidation catalyst located upstream or downstream of aturbocharger). As the effective thermal inertia of the multipleoxidation catalysts and the SCR catalyst is reduced by the additionalheat energy received from the engine, the time at which the light-offtemperature of the exhaust treatment system is achieved. This may resultin lower light-off times for both the oxidation catalysts and the SCRcatalysts, which in turn may result in a reduction of the amount ofemissions that are subsequently released to the surrounding environmentduring the initial start-up phase of engine 110. Additionally, thisincreased thermal efficiency may reduce the need for parasitic rapidwarming conventions (that reduce overall fuel economy) that may use fuelfor heating purposes.

As illustrated in FIG. 1, the separated exhaust flows may be re-combinedwithin a second, downstream flow combining passage 167. Although shownas combining two separated exhaust gas flows that are received fromexhaust separation passage 165 (and oxidation catalysts 134 and 136), inother embodiments, downstream flow combining passage 167 may receivethree or four separated exhaust gas flows and combine them into a singlere-combined exhaust gas flow. The re-combined exhaust gas flow may thenbe received by turbocharger 166 and SCR catalyst 140. Prior to beingreceived by turbocharger 166 and SCR catalyst 140, however, a liquidreductant, such as urea, may be injected into the re-combined exhaustgas flow. SCR catalyst 140 may utilize the liquid reductant (such as anaqueous urea solution) that is injected into the exhaust gases upstreamof SCR catalyst 140. Prior to reaching the SCR catalyst, the waterdroplets within the injected solution may evaporate. The remaining ureacomponent then hydrolyzes and decomposes into ammonia which then entersthe SCR catalyst via the exhaust gas flow stream. A catalyst within theSCR catalyst facilitates a reaction between the NOx component of theexhaust gas flow stream and the ammonia to break down the NOx into watervapor and nitrogen gas. The efficiency of this NOx reduction may bedirectly proportional to the degree of vaporization of the aqueous ureasolution and uniformity of the distribution of the resulting ammoniawithin the engine exhaust gases upstream of the SCR catalyst.

The degree of vaporization and the uniformity of the distribution of theresulting ammonia within the exhaust gases upstream of the SCR catalystmay be increased by funneling the exhaust gases (with liquid reductantsuspended therein) through turbocharger 166 prior to passing themthrough SCR catalyst 140. The impingement of the exhaust gases upon therotating blades integral and internal to turbocharger 166 may aid in thebreakdown of the injected urea (suspended within the exhaust gases) intoammonia and in the uniformity of distribution of the ammonia dropletssuspended within the exhaust gases. In some embodiments, the bladeswithin turbocharger 166 may be coated with hydrolysis catalyst or SCRwashcoat that may further enhance the breakdown of urea into ammonia.The exhaust gas flow may then be received from turbocharger 166 by SCRcatalyst 140. Note that SCR catalyst 140 can include various SCRcatalysts for reducing NOx or other products of combustion resultingfrom the combustion of fuel by engine 110. In some embodiments, aparameter of the reductant injection may be controlled by an electroniccontroller (not shown in FIG. 1). For example, reductant injectionpressure, and/or injection volumetric flow rate, and/or the overallamount of reductant per injection may be varied via an electroniccontroller. As a non-limiting example, in some embodiments, the amountof reductant injected may be varied by the electronic controller inresponse to turbocharger operating speed. For example, since theresidency time of the reductant in proximity to SCR catalytic materialmay vary with turbocharger speed, it may be advantageous to adjust theamount of reductant injected with turbocharger speed.

Note that with regards to vehicle applications, exhaust system 100 maybe arranged on the underside of the vehicle chassis. Additionally, itshould be appreciated that the exhaust passage portions coupling thevarious exhaust system components may include one or more bends orcurves to accommodate a particular vehicle arrangement. Furthermore, thecross-sectional shapes of the various exhaust system components and theexhaust passage portions that couple the various exhaust systemcomponents may be circular, oval, rectangular, hexagonal, or any othersuitable shape. Further still, it should be appreciated that in someembodiments, exhaust system 100 may include additional components notillustrated in FIG. 1 or may omit components described herein.

FIG. 2 illustrates a side view of exhaust treatment region 135 ingreater detail as a longitudinal cross-section. Injector 202 is showncoupled to a wall of downstream flow combining passage 167 by aninjector boss 204. Injector 202 can inject, through an opening in thewall of the flow combining passage, a liquid supplied to it in responseto a control signal received via a communication line (not shown inFIG. 1) from an electronic control system of engine 110.

As illustrated, injector 202 can inject the liquid at an angle ofincidence that is substantially perpendicular to the direction of theseparated exhaust flows ejected by oxidation catalysts 134 and 136. Inother embodiments, injector 202 may inject liquid at an angle ofincidence with respect to the direction of flow of one of the separatedexhaust flows ejected by one of the oxidation catalysts that is greaterthan or less than ninety degrees. As non-limiting examples, injector 202may inject liquid into one of the separated exhaust flows at an angle ofincidence of 45°, 65°, 80°, or 120°. However, it should be appreciatedthat other angles may be utilized. In yet other embodiments, injector202 may be located at a location on downstream flow combining passage167 downstream of the point at which the separated exhaust flows arere-combined into a re-combined exhaust gas flow and upstream of thepoint at which the re-combined gas flow enters turbocharger 166. In yetother embodiments, injector 202 may be arranged such that liquidreductant may be injected directly into turbocharger 166. This may allowfor reductant to impinge upon the blades of the turbocharger at agreater velocity that may increase the break-up and dispersion of thereductant within the combined exhaust gas flow.

Likewise, although shown in FIG. 2 as a substantially orthogonal angle,the angle between the direction of flow of a separate exhaust gas flowejected by an individual oxidation catalyst and the direction of flow ofthe re-combined exhaust gas within flow combining passage 167 may be anon-orthogonal angle in other embodiments. For example, in otherembodiments, the angle between the direction of flow of a separateexhaust gas flow ejected by an individual oxidation catalyst and thedirection of flow of the re-combined exhaust gas flow may be 95°, 105°,120°, or 150°. The spray pattern provided by injector 136 may include avariety of patterns for improving the evaporation rate and dispersion ofthe liquid reductant within the exhaust gas flow stream. For example, aninjector can provide spray patterns that are configured as sheets,solids, or hollow cones. However, it should be appreciated that variousother suitable spray patterns and/or shapes may be utilized.Additionally, the spray provided by an injector may be configured assubstantially a liquid spray (i.e., no substantial amount of gas(es)entrained therein). In other embodiments the spray provided by aninjector may be configured as an air-assisted spray (i.e., air entrainedtherein).

In some examples, geometric constraints associated with an exhaustsystem for a vehicle may increase the rate at which mixing andevaporation of the injected liquid reductant within the exhaust gas flowstream are to be performed so that the liquid spray is finely atomizedprior to being absorbed by the catalyst. Further, some exhaust systemconfigurations may require that the drops of liquid within the spray beless than a particular size to achieve a particular rate of evaporationand/or mixing of the liquid into the exhaust gases. As one non-limitingexample, the drops of liquid within the spray may be less than 40microns in diameter, for some exhaust systems. However, the price of aninjector may increase in proportion to a decrease in the size of thedrops of liquid provided by the spray. Thus, in order to reduce cost ofthe injector, it may be desirable to improve mixing and evaporationrates so that an injector that produces a spray that is comprised oflarger drops of liquid may be used.

As described above with regard to FIG. 2, the impingement of the exhaustgases upon the rotating blades integral and internal to turbocharger 166may aid in the breakdown of the injected urea (suspended within theexhaust gases) into ammonia and in the uniformity of distribution of theammonia droplets suspended within the exhaust gases. As mentioned above,in some embodiments, the blades of turbocharger 166 may be coated with ahydrolysis catalyst coating to enhance the breakdown of injected ureainto ammonia. In some embodiments, the blades of turbocharger 166 may becoated with selective catalytic reduction (SCR) washcoat that mayenhance the breakdown of injected into ammonia and enhance NOxconversion. The SCR washcoat layer may be applied to each turbochargerblade after the blades are subjected to a heat and/or chemical surfacetreatment. As such, the size and hence the overall cost of thedownstream SCR catalyst 140 may be reduced. In some embodiments, theaddition of an SCR washcoat layer on the blades of turbocharger 166 mayallow for a filter substrate integral to DPF 142 to be coated with SCRwashcoat and as such, allow for removal of NOx and particulate mattersans an SCR catalyst or with a smaller SCR catalyst. The overall cost ofthe exhaust treatment system may thereby be reduced.

As mentioned above, by virtue of arranging oxidation catalysts 134 and136 upstream of turbocharger 166, both the oxidation catalysts and SCRcatalyst 140 may be arranged in closer proximity to engine 110. As such,the light-off times of both oxidation catalysts and the SCR catalyst maybe decreased due to increased amount of heat energy received by thecatalysts from the engine. Additionally, these reduced light-off times,in concert with improved SCR NOx conversion efficiency may allow forhigher feedgas NOx emissions. In other words, the exhaust gascirculation (EGR) rate may be reduced at light engine loads, fueleconomy and engine transient response may be improved, and the workloadof turbocharger 166 may be reduced.

FIG. 3 illustrates a process flow for the transporting and treating ofexhaust gases by exhaust system 100. At 302, exhaust gases ejected byindividual cylinders of engine 110 may be combined into a single exhaustgas flow. At 304, the single exhaust gas flow may be separated intoseparate exhaust gas flows. At 306, the separate exhaust gas flows mayeach be passed through a separate oxidation catalyst. At 308, theseparate exhaust gas flows may be received from the oxidation catalystsby a flow combining passage where they may be re-combined into a singlere-combined exhaust gas flow. At 310, a liquid reductant may be injectedinto the re-combined exhaust gas flow. It should be appreciated that insome embodiments, however, liquid reductant may be injected upstream ofthe flow combining passage (i.e., prior to the separate exhaust gasflows being re-combined). In other words, liquid reductant may beinjected into an individual separate exhaust gas flow or may be injectedinto multiple separate exhaust gas flows prior to the separate exhaustgas flows reaching the flow combining passage.

At 312, the re-combined exhaust gas flow may be passed through aturbocharger. As discussed above, the impingement of the re-combinedexhaust gas flow (with injected liquid reductant injected therein) uponthe blades of the turbocharger at 312 may aid in the breakdown of theliquid reductant into ammonia. Correspondingly, the efficiency of NOxconversion at 312, where the re-combined exhaust gas flow is passedthrough a SCR catalyst, may be increased.

It should be appreciated that the configurations disclosed herein areexemplary in nature, and that these specific embodiments are not to beconsidered in a limiting sense, because numerous variations arepossible. The subject matter of the present disclosure includes allnovel and nonobvious combinations and subcombinations of the varioussystems and configurations, and other features, functions, and/orproperties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1-20. (canceled)
 21. An engine exhaust gas treatment system, comprising:an injector directing a spray of reductant into exhaust gas; an exhaustmanifold leading to a first flow combining passage that combines exhaustgases from a plurality of cylinders into an exhaust gas flow; an exhaustseparation passage, downstream of the first flow combining passage, thatseparates the exhaust gas flow into a plurality of separate exhaust gasflows; a plurality of oxidation catalysts, each of which receives one ofthe pluralities of separate exhaust gas flows; a second, downstream,flow combining passage that receives the plurality of separate exhaustgas flows and combines them into a re-combined exhaust gas flow; aturbocharger that receives the re-combined exhaust gas flow; and aselective catalytic reduction catalyst positioned downstream of theturbocharger.
 22. The system of claim 21, wherein blades of theturbocharger are coated with a hydrolysis catalyst.
 23. The system ofclaim 21 wherein blades of the turbocharger are coated with a selectivecatalytic reduction washcoat.
 24. The system of claim 21, wherein theinjector is configured to direct the spray of reductant into theturbocharger.
 25. The system of claim 21, wherein the injector isconfigured to direct the spray of reductant into the re-combined exhaustgas flow upstream of the turbocharger.
 26. The system of claim 21,wherein the injector is configured to direct the spray of reductant intoat least one of the plurality of separate exhaust gas flows, downstreamof one of the plurality of oxidation catalysts.
 27. The system of claim21, wherein the exhaust gas flow that is separated by the exhaustseparation passage is received by the exhaust separation passage fromthe engine.
 28. The system of claim 21, wherein re-combined gas flow isreceived by the turbocharger from the first flow combining passage. 29.The system of claim 21, further including a controller that adjusts theamount of reductant injected in response to turbocharger operatingspeed.
 30. A method of treating engine exhaust gases, comprising:spraying reductant into the exhaust gases; combining, separating, andthen re-combining exhaust gases, the exhaust gasses flowing throughseparate oxidation catalyst when separated; reacting the re-combinedexhaust gases with a hydrolysis catalyst coated on turbocharger bladesduring expansion through the turbocharger; and passing the expandedre-combined exhaust gas flow through a selective catalytic reductioncatalyst.
 31. The method of claim 30, further comprising directing thespray of reductant into the turbocharger.
 32. The method of claim 30,further comprising directing the spray of reductant into the re-combinedexhaust gas flow upstream of the turbocharger.
 33. The method of claim30, further comprising directing the spray of reductant into at leastone of the plurality of separated exhaust gas flows, downstream of theseparate oxidation catalyst from which the one of the separated exhaustgas flows was ejected.
 34. The method of claim 30 wherein the reductantis injected at an angle of incidence that is substantially perpendicularto a direction of the separated exhaust flows ejected by each oxidationcatalyst.
 35. The method of claim 30 wherein the reductant is injectedat an angle of incidence with respect to a direction of flow of one ofthe separated exhaust flows ejected by one of the oxidation catalyststhat is less than perpendicular.
 36. A method of treating engine exhaustgases, comprising: spraying reductant into the exhaust gases; combining,separating, and then re-combining exhaust gases, the exhaust gassesflowing through separate oxidation catalyst when separated; reacting there-combined exhaust gases with a selective catalytic reduction washcoatcoated on turbocharger blades during expansion through the turbocharger;and passing the expanded re-combined exhaust gas flow through aselective catalytic reduction catalyst.
 37. The method of claim 36,further comprising directing the spray of reductant into theturbocharger.
 38. The method of claim 36, further comprising directingthe spray of reductant into the re-combined exhaust gas flow upstream ofthe turbocharger.
 39. The method of claim 36, further comprisingdirecting the spray of reductant into at least one of the plurality ofseparated exhaust gas flows, downstream of the separate oxidationcatalyst from which the one of the separated exhaust gas flows wasejected.
 40. The method of claim 36 wherein the reductant is injected atan angle of incidence that is substantially perpendicular to a directionof the separated exhaust flows ejected by each oxidation catalyst.